Design and Experimental Validation of a Sweet Potato Seedling Transplanting Mechanism Based on a Non-Circular Planetary Gear Train and Fourier Series Synthesis

To address the high cost, structural complexity, and poor horizontal transplanting performance of existing sweet potato seedling transplanting mechanisms, this study proposes a Fourier series-based kinematic synthesis method and designs a non-circular gear planetary transplanting mechanism, which is then validated through virtual simulation and prototype testing. Based on the agronomic requirements for horizontal transplanting, key positions including seedling pick-up, soil entry, and soil exit are identified. The complex vector method is applied to establish a 2R open-chain kinematic synthesis model with trajectory and posture error equations, from which the optimal mechanism parameters are derived. Kinematic modeling of the non-circular gear planetary train is conducted, and auxiliary design software is developed to generate the pitch curves of the non-circular gears. A cylindrical cam mechanism is designed for seedling gripping and release. Structural design and virtual prototyping are completed, and simulations verify the theoretical model. A physical prototype is manufactured for kinematic and field testing. The results demonstrate high consistency among the measured, simulated, and theoretical trajectories, with a maximum deviation of 0.6° (relative error of 0.83%) at the key posture positions. At rotational speeds of the transplanting mechanism of 30 r/min and 40 r/min, the average transplanting success rates reach 91.2% and 81.2%, respectively, while the planting depth, horizontal underground length, and plant spacing all satisfy the agronomic requirements, confirming the feasibility of the proposed design. This study provides a theoretical and technical foundation for the development of a high-performance sweet potato seedling transplanting mechanism.